JAY GRIMES: Climate change and disease

This page has carried several contributions about the environmental and socioeconomic impacts of climate change. The purpose of this contribution is to discuss the effect of climate change (warming) on human infectious disease.

These diseases can be directly transmitted from human to human(s). Some are transmitted by fomites (shared articles such as combs, clothing, drinking glasses), and some are transmitted by vectors (e.g., ticks, fleas, mosquitoes, copepods). All of these modes of transmission are affected by climate change.

Here I write about the primary marine Vibrio bacteria that cause diseases in humans, Vibrio cholerae, V. parahaemolyticus and V. vulnificus. The ecology and epidemiology of these three have been the focus of my research since the 1980s. These three Vibrios can be transmitted by all three modes of transmission, and they are also found in oysters. They cause diarrheal disease and wound infections.

Vibrio cholerae causes 3 million to 5 million cases of cholera with 100,000 to 120,000 deaths annually, with the center of infections occurring in Africa. There are only 5-10 cases of cholera in the U.S. annually.

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Vibrio parahaemolyticus causes about 4,500 infections (usually diarrheal disease) in the U.S. each year, but deaths are rare.

Vibrio vulnificus causes, on average, about 95 cases, 85 hospitalizations and 35 deaths in the U.S. each year. Many experts believe V. vulnificus is the most virulent bacterium known and that it has, on average, a 50 percent fatality rate.

All three of these Vibrios are affected by climate change. Rita R. Colwell, University of Maryland, is a world-renowned expert on cholera and believes global warming is causing an increase in the incidence of this disease (chgeharvard.org/resource/infectious-diseases-changing-planet).

In 2004, there was an outbreak of V. parahaemolyticus aboard an Alaska cruise ship. Of 189 passengers, 62 patients had this Vibrio (29 percent attack rate), as did all oysters tested. The oysters came from an oyster farm in Prince William Sound where mean water temperatures had been increasing (0.21 degrees Celsius per year) since 1997. In 2004, mean daily temperatures in the sound did not drop below 15 degrees Celsius, and this is the temperature required for V. parahaemolyticus to begin growing in seawater and in oysters. This outbreak pushed the known range of V. parahaemolyticus -- previously thought to be the Pacific Northwest -- 620 miles north!

The Vibrio most feared on the Gulf Coast is Vibrio vulnificus. This Vibrio causes necrotizing fasciitis, referred to a "flesh-eating disease," of the extremities. The disease progresses rapidly and often requires amputation of the limb, and even then it can cause death. According to the Food and Drug Administration, 90 percent of all V. vulnificus illnesses in the U.S. result from consumption of raw Gulf Coast oysters.

Gastroenteritis caused by V. vulnificus is relatively mild and usually self-limiting in otherwise healthy patients, as is the case for wound infections. However, in patients at risk, gastrointestinal disease and wound infections can progress to septicemia, which can further and rapidly develop into necrotizing fasciitis. Immune disorders, especially chronic liver disease, place patients at risk for developing this serious, life-threatening disease. As is the case with most of the Vibrios (there are close to 100 species), the abundance of V. vulnificus in oysters and water increases with temperature.

Recent work reported by the FDA lab on Dauphin Island, Alabama, has noted an expansion of V. vulnificus illnesses associated with oysters harvested from the Gulf of Mexico in April and November since 1998. On average, the CDC reports there are approximately 50 cases in the Gulf region each year.

Contact Jay Grimes, professor of marine microbiology at the Gulf Coast Research Laboratory's Cedar Point campus, at jay.grimes@usm.edu.